Vibrating reed device



March 30, 1954 L. s. BOSTWICK VIBRATING REED DEVICE 2 Sheets-Sheet 1 Filed Oct. 19, 1950 lNl ENTOR By L. G. BOSTW/CK ATTORNEY March 30, 1954 gos'rw cK 2,673,482

VIBRATING REED DEVICE Filed Oct. 19, 1950 2 Sheets-Sheet 2 THIS PORTION CLAMPED BETWEEN COPPER PLATES FOR HEAT mun/vs I FREQUENCY- TEMPERA TURE CHARACTERISTICS OF .3483

Nl-SPAN FOR/(S IN LOW FLUX SELECTOR-S DEG. DEG. c. F.

so I76 800 F BAKE 6= -/5x I0 I40 5/ 800/-' BAKE WITH 40 %"A-AL0 TIPS 77 52 2o QUENCH ANNE/4L ,6=+22.5x/0- CYCLES 25R sc0-0 N VE N TOR L. G. TW/CK A TTORNE Y Patented Mar. 30, 1954 UNITED STATES PATENT OFF ICE VIBRATING REED DEVICE Lee .G. .Bostwick, .Florham Park, 3., :assignor to .Bell Telephone Laboratories, Incorporated, .New York, N. Y., a corporation of New York Application October 19, 1950, Serial No. 191,027

4-,Claims. 1

This invention relates to devices including magnetic vibrating reeds and more particularly to such-devices wherein it is especially important that the resonance frequency of the reed or reeds remain substantially constant over a range of operating temperatures.

The resonance frequency of a vibrating reed or reeds such as clamped-free cantilevers, tuning forks or other forms is subject to variation with changes in temperature. This variation may be caused by several factors. First the dimensions of the reed are changed in accordance with the temperature coefficient of expansion-of the reed material and this usually causes the resonance frequency to increase with rising temperatures. A temperature change also causes a change in the elastic modulus of the reed material, which enters into the frequency equation of the reed in a Well-known manner. If the reed is electromagnetically driven, the resonance frequency may be materially altered by a change in the magnetic flux in the gap across which the driving force for the reed is developed. This gap flux change is caused by permeability and coercive force changes which in turn are caused by temperature changes in the reed material.

One object of this invention is to maintain the resonance frequency of the reed or reeds in vibrating reed devices substantially constant over a range of operating temperatures.

.In accordance with .one broad feature of this invention, the reed is constructed so that the effective thermoelastic coefiicient of the reed as a'wholeis of a value to compensate for the effects of the temperature coefficient of expansion, specificallyand for .exampleis substantially equal and opposite in sign to the temperature coefficient of expansion.

.In accordance with a more specific feature of the invention, the reed of a suitable alloy .having a prescribed thermoelastic coeiiicient is first heat treated to relieve internal .strains and stresses, at'a temperature that does not appreciably :alter its thermoelastic properties. A portion of the reed is thenvheated to a higher temperature and quenched without greatly heating the remaining portion of the reed. This is accomplished as .by clamping the remaining portion .of the reed between relatively massive blocks of a good heat conducting material, such as copper,

and inserting the unclamped portion in ianfinduction heating coil :or in a locally applied gas flame. This higher temperature theatment anneals the treated portion of the. reed, thereby increasing its magnetic permeability and reducing the coercive force .so that these factor-shave less effect on the gap flux and frequency with temperature changes. The high temperature treatment also changes the thermoelastic coefficient of the material but only so 'much of the reed is annealed that the thermoelastic coemcient .of the treated portion of the reed results in an oven-all eflective therm'oelastic coeflicient of the reed as a whole substantially equal in magnitude, but opposite in sign, to the temperature 'coeflicient of expansion of the reed 'material.

These and other objects and features :of the invention will be more clearly understood from the following detailed description when read in conjunction "with the drawing, in which:

Fig. 1 is an elevational view partly in section of a vibratingzreed device, illustrativeof one embodiment of this invention.

Fig. 2 is a view similar to Fig. 1 but taken at right angles thereto;

Fig. 3 is a front view of a reed or tine in the device of Fig. -1:

Fig. 4 is a side viewof theireed; and

Fig. 5 is a graph showing the frequency characteristics of reeds given different heat treatments.

Referring now to Fig. 1 the tines Illand l I are mounted on :either side of spacer l2 as-by brazing. Secured to the tines 1-0 and ll by rivets 13 and M are washers t5 and 1-6 which extend through an aperture 1 I in insulating spacer I 8. This spacer has an outside diameter slightly less than the inside diameter of envelope 19, thus allowing the tine assembly "limited freedom of motion within the envelope $9. This assembly is secured by the rivets l3 and M to one end of conducting bar =20 which in tu-rn is secured near its other end by conducting element '2! positioned around stud 2-2. The extreme low-er end of conducting bar 20 sets into slot 23 -of end plug '24. It is to b noted that the cross-sectional "area of 'slot 2-3 is larger than the crosssectional area of conducting bar 20, thus allowing the conducting bar 20 "to 'move freely within slot 23. It can thus be seen that the tine assembly is floatably "mounted to prevent any bending or distortion of the assembly within the housing.

The contact support .and spring assembly .2-5 is securedon the stud 22 1)) nutrZB. This.assembly comprises an insulating spacer block 21, spring wires 28 and 29 shown in Fig. 2, support spring 30 through whichspring wires -2"B--a-n-d 2'9 are secured by suitable tension "means. The spring 30 rests in a slot 3| in contact bar '2 0,. Supported by'insu'la'tin'g block '21 is a double wire assemb1y32 to which contact "33 is affixed as by soldering. One of the wires of the double wire assembly 32 is terminated with the end 34 thereof bent perpendicular to the contact 33. The spring contact 33 extends ill-1S1; beyond the tuning bar 35 and is spaced a short-distance therefrom. During "vibration ot the *tine H), the tuning bar 35 which is fastened thereto will make contact with the spring contact 33.

A permanent magnet 35 is secured to bar 2t. Adjacent the permanent magnet 30 is located pole-piece 37! which extends through electromagnetic damping members such as copper sleeves 10 to a position between the ends of the reeds or tines i and II.

The reeds or tines are shown in detail in Fig. 3. Tuning bars 35, 55 and 5B are secured to the reed as by spot welding, for example, and may be adjusted by bending to impart the desired frequency of vibration to the reed I0. Holes 51 and 53 provide means for mounting the reed.

The contact separation can be adjusted by the nut which can be moved along the stud 22 thus causing a variation of the distance of sprin contact 33 from tuning bar 35 by means of the lever action of double wire 32. I

The tines or reeds I0 and H may be set in vibration by energization of a magnetic coil 47 mounted exterior of and extending around the envelope i0. Magnetic coil H is partially enclosed in a magnetic shell 5 l. The magnetic cirsuit of permanent magnet 35 extends through pole-piece t'l, tines l0 and ii, through magnetic shell 5i and back to permanent magnet 30. Thus the portion of the pole-piece Lil positioned between the tines l0 and H has a definite polarity due to permanent magnet 3 Consequently, when the tines l0 and H are magnetized by external coil dl they will either be attracted to the pole-piece 3! or will be repelled from the polepiece 2'! depending upon the polarity of magneti zation of the tines.

When contact is made between spring contact 33 and tuning bar 35, an electrical circuit may be traced in Fig. 2 from conductor 4%] through solder joint double wire assembly 132, spring contact tuning bar 35, tuning fork tine l0, metal spacer 42, metal washer E55, conducting bar 20, and element 2| which terminates in terminal pin 43. Terminal pins 4 3 and d3 are sealed as by solders and Ail respectively which secure conductor 40 and conducting strip 21 respectively.

It is important in a number of applications of vibrating reed devices of the type described that the reeds be responsive substantially, only to energizing forces of a prescribed frequency or with in a restricted frequency range. To this end, the reeds in such devices heretofore have been tuned mechanically at a, preassigned frequency. However, as has been pointed out hereinabove, the resonance frequency of the reed is subject to variation with temperature. In accordance with this invention, such variation is minimized or substantially prevented. The manner in which this is efiected will be understood from consideration of a specific embodiment.

The tines or reed l0 and I l in this embodiment of the vibrating reed device described herein had a composition approximately as follows:

The alloy used in the specific embodiment may be annealed, formed into metal tape, and cut into lengths to be used as the reeds or tines. The

strip material initially is not sufiiciently mechanically stable due to large residual internal stresses. To relieve these stresses, the material is heat treated, without deleteriously affecting its magnetic properties. In a specific case for example, it may be rolled and heated for three hours at a temperature of the order of 800 F. or at a temperature of the order of 600 F. for about twentyfour hours. As so processed, the material is mechanically stable, has a high yield strength, and is suitable mechanically for use in reeds. The thermoelastic coefiicient, however, is not properly related to the expansion coeflicient so as to maintain constant frequency with variations in temperature. Furthermore, the magnetic properties of these reeds are not favorable because the permeability is low and variable with temperature, and because the coercive force of the reeds is sufficiently large to materially alter the gap flux, and therefore the reed resonance frequency, when the reed strikes the pole-piece and becomes, to some extent, permanently magnetized.

To avoid these magnetic shortcomings of the reeds and to make their thermoelastic coeificient substantially equal to their expansion coeflicient, one end of the tines is annealed to leave them in a soft state This increases the permeability of the reeds several fold and reduces the coercive force to a small fraction of its previous value in the tip section of the reed where the magnetic properties are most important.

For the alloy treated as noted above, specifically when heated for about twenty-four hours or more at a temperature of 600 F. or about one hour or more at a temperature of about 800 R,

to relieve internal stresses and strains, the alloy is found to have a thermoelastic coefficient of approximately 15 10- The alloy when heated to about 1800 F. and

- quenched, has a positive thermoelastic coeficient of approximately +22.5 10- per degree F. A coefficient for the reed as a whole between these two values is required because the temperature coefiicient of expansion of the alloy is about +l.5 10 per degree F. and the over-all thermoelastic coefficient should be approximately equal to this and of opposite sign. To obtain the proper coefficient for the reed as a whole, the base end of the reed is clamped between good heat conductin plates, such as of copper, and the other end portion of the reed is annealed without affecting the remainder. Specifically, the other end is inserted in a coil of an induction heat furnace, brought to a temperature of about 1800" F. and then quenched in water. ihe copper blocks prevent the remainder of the reed from heating substantially. The annealed tips of the tines have a thermoelastic cocfiicient of about +22.5 l0* which has the eiiect of reducing the thermoelastic coefiicient of the reed as a whole and making it more nearly compensate for the effect of the temperature coefficient of expansion. Furthermore, the ends of the tines have a higher permeability due to the annealing and also have lower coercive force.

The magnitude and character of the effect of heat treating in a particular case are indicated in Fig. 5 which shows the frequency variation with temperature in a ZOO-cycle vibrating reed device, with the magnet strength reduced to a low level such that only elastic modulus effects are present. Three devices are represented as follows, for reeds of a length of about 1.5 inches:

1. Curve 50 shows frequency-temperature characteristics of reeds rolled and heated three hours at 800 F.

2. Curve shows frequency-temperature characteristics of similar reeds with of the tips annealed at a temperature of 1800 F.

3. Curve 52 shows frequency-temperature characteristics of reeds quench annealed over the full length.

The effective themoeiastic coefficient, [3, for each case is indicated on the curves. From these curves the improvement realized by the treatment above described is evident. Although for the case illustrated in Fig. 5, exact compensation for the temperature coeflicient of expansion is not realized, it has been found that for many practical purposes, compensation of the magnitude indicated is adequate. In typical devices constructed in accordance with this invention, the resonance frequency of the reeds is maintained constant within :0.05 per cent over an operating temperature range of -40 F. to +180 F.

It is to be understood that the embodiment of the invention herein described is but illustrative thereof and that various changes may be made therein without departing from the scope and spirit of the invention. For example, other materials such as nickel iron alloys containing small amounts of molybdenum may be used and different baking and annealing temperatures employed for these alloys. Also various lengths of the reeds may be treated, it being noted that by annealing a greater length the over-all thermoelastic coefficient is made more positive.

What is claimed is:

1. The method of processing a pressure formed reed having the composition substantially 48 per cent iron, 42 per cent nickel, 6 per cent chromium and 2 per cent titanium, which method comprises heating said reed at a temperature of about 800 F. for about three hours to relieve stresses and strains developed in the reed during the forming thereof, and treating one end portion of said reed to alter the thermoelastic coefficient of said portion such that the effective thermoelastic coefficient of said reed as a Whole is substantially equal'and of opposite sign to the temperature coefiicient of expansion of said reed, said treating comprising heating said end portion to a temperature of about 1800 F. and quenching said portion.

2. The method of processing a pressure formed reed having a composition substantially 48 per cent iron, 42 per cent nickel, 6 per cent chromium and 2 per cent titanium, which comprises heating said reed at a temperature of about 800 F. for about three hours to relieve stresses and strains developed in the reed during the forming thereof, mounting said reed in a heat conducting body with a tip portion of said reed exposed, treating said tip portion to alter the thermoelastic coefiicient of said portion such that the effective thermoelastic coefficient of said reed as a whole is substantially equal and of opposite sign to the temperature coefiicient of expansion of said reed, and removing said reed from said heat conducting body, said treating comprising heating the tip portion only to a temperature of about 1800 F. and quenching said portion.

3. A reed for a vibrating reed device comprising a metallic strip having a composition of substantially 48 per cent iron, 42 per cent nickel, 6 per cent chromium and 2 per cent titanium, said strip having a pair of portions including a body portion having a negative thermoelastic coefficient and a tip portion having a positive thermoelastic coeflicient, said coefficients being correlated to provide a thermoelastic coefficient for the entire reed of a preassigned' value intermediate the thermoelastic coefficients of the body and tip portions.

4. A reed in accordance with claim 3 wherein said body portion has a thermoelastic coefficient of about -15 10* said tip portion has a thermoelastic coefiicient of about {22.5 10 and the composite thermoelastic coefficient for the entire reed is substantially equal and of opposite sign to the temperature coefiicient of expansion of the reed.

LEE G. BOSTWICK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 203,228 White Apr. 30, 1878 569,143 Wheeler Oct. 6, 1896 1,715,324 Haglund May 28, 1929 1,880,923 Eisenhour Oct. 4, 1932 2,236,158 Rockefeller, Jr. Mar. 25, 1941 2,246,078 Rohn et a1 June 17, 1941 2,309,714 Radtke et al. Feb. 2, 1943 2,327,129 Ronan Aug. 17, 1943 2,331,870 Coxe Oct. 12, 1943 2,419,825 Dinerstein Apr. 29, 1947 2,489,400 Cooley Nov. 29, 1949 2,500,372 Noble Mar.,14, 1950 2,502,339 Perreault Mar. 28, 1950 2,505,633 Whaley Apr. 25, 1950 2,533,736 Lohr Dec. 12, 1950 2,561,732 Fine July 25, 1951 2,587,236 Side Feb. 26, 1952 FOREIGN PATENTS Number Country Date 723,332 France Jan. 13, 1932 

1. THE METHOD OF PROCESSING A PRESSURE FORMED REED HAVING THE COMPOSITION SUBSTANTIALLY 48 PER CENT FROM, 42 PER CENT NICKEL, 6 PER CENT CHROMIUM AND 2 PER CENT TITANIUM, WHICH METHOD COMPRISES HEATING SAID REED AT A TEMPERATURE OF ABOUT 800* F. FOR ABOUT THREE HOURS TO RELIEVE STRESSES AND STRAINS DEVELOPED IN THE REED DURING THE FORMING THEREOF, AND TREATING ONE END PORTION OF SAID REED TO ALTER THE THERMOELASTIC COEFFICIENT OF SAID PORTION SUCH THAT THE EFFECTIVE THERMOELASTIC COEFFICIENT OF SAID REED AS A WHOLE IS SUBSTANTIALLY EQUAL AND OF OPPOSITE SIGN TO THE TEMPERATURE COEFFICIENT OF EXPANSION OF SAID REED, SAID TREATING COMPRISING HEATING SAID END PORTION TO A TEMPERATURE OF ABOUT 1800* F. AND QUENCHING SAID PORTION. 